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"The fraction of retrieved documents that are in fact interesting is called the precision. The fraction of all interesting documents the search engine in fact retrieves is called the recall"
Can someone tell me what's the difference between these two sentence??
Please explain in details to make me understand! Thanks.

Jaleh · Accepted Answer

Oh I understood it. thanks<img class='emoticon' style='Width:19px;Height:19px;' data-delaysrc='https://uat-englishforward-forums-backend.s3.us-west-2.amazonaws.com/Emoticons/10.gif' src='https://uat-englishforward-forums-backend.s3.us-west-2.amazonaws.com/Emoticons/10.gif' alt='Emotion: embarrassed'/>

AlpheccaStars · Answer

Read this article: https://en.wikipedia.org/wiki/Precision_and_recall

Suppose there are 100,000 documents in the search space.
You make a search on these documents. Suppose that the perfect search engine would find 200 matching documents. All these 200 would be interesting. This is the "interesting" set. All the remaining 99,800 are irrelevant (not "interesting").

But you are not using a perfect search engine. You are using a real search engine, which is not perfect.
Your search engine will return some documents from the 200 "interesting" set, but also some that are in the set 99,800 (not "interesting" or irrlevant)

You can measure how good your search engine is. There are two measures, precision and recall. These are percentages. A perfect search engine would score 100% on each measure.

Case 1. Suppose your search engine retrieves 100 documents. But 20 of these are not in the "interesting" set. The precision is 80%. (80 of the 100 documents are from the interesting set.)
But you search engine missed a lot of "interesting" documents. Since your search engine returned 100 (80 "interesting" and 20 "not interesting"), the Recall is 80/200, or 40%.

Case 2. Your search engine retrieves 500 documents. It gets all 200 from the "interesting" set, but 300 that are not relevant. The precision is 200/500, or 40%. The recall is 100%. So it had perfect recall, but it was not very precise.

Case 3.
Suppose your search engine retrieves 250 documents. It gets 199 from the "interesting" set, and 51 that are not interesting. The precision is 199/250 - about 80%, and its recall is 199/200 - over 99%.

Of course, a real search engine will have a range of values for precision and recall, depending on the particular search.

Jaleh · Answer

Many many thanks dear AlpheccaStars<img class='emoticon' style='Width:19px;Height:19px;' data-delaysrc='https://uat-englishforward-forums-backend.s3.us-west-2.amazonaws.com/Emoticons/63.gif' src='https://uat-englishforward-forums-backend.s3.us-west-2.amazonaws.com/Emoticons/63.gif' alt='Emotion: rose'/>

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